August 15, 2013 — University of Wyoming Geologist Neil Humphrey and colleagues
have taken a significant step to better understand glacial movement in
Greenland, which is fundamental to projecting future sea-level rise worldwide.
The key may lie in the effect of the basal or sub-glacial drainage system on
the Greenland ice sheet.

Sub-glacial drainage systems are formed from the hydraulic
pathways that contain and transfer water located close to the contact between
an ice mass and its substrate.

But rather than the melting ice draining out from under the
ice sheet within a matter of days -- as a decades-old theory of a glacial river
or conduit system purports -- the melting ice moves much more slowly, as ice melts
from everywhere on the ice sheet and meltwater moves underneath in what Humphrey terms a “distribution system.”

“It’s socially relevant science. It’s directly related to
sea-level rise,” says Humphrey, a UW professor in the Department of Geology and
Geophysics. “From a human perspective, 20 percent of the world’s population
lives within 50 feet of sea level. If Greenland is to melt, it’s beyond
catastrophic.”

Humphrey is co-author of a paper, titled “Basal Drainage
System Response to Increasing Surface Melt on the Greenland Ice Sheet,” that
will be published in this month’s issue of Science.
This marks the fifth time he has contributed a paper that has been published in
Science, Humphrey says.

Toby Meierbachtol, a doctoral student at the University of
Montana, is the paper’s lead writer.
Joel Harper, an associate professor in the Department of Geosciences at
the University of Montana, was the other contributing writer. Humphrey and
Harper have worked as colleagues in the field for 20 years.

Drilling Down

During the summers of 2010-12, the research group used hot
water methods to drill 23 vertically straight bore holes into the ice sheet bed
-- in ice up to 1 kilometer thick -- at sites along an east-west transect in
western Greenland.

Humphrey designed and constructed a hot water drill at UW.
The drill pumps cold surface water through a series of heaters and high-pressure
pumps to melt a hole -- at 120 meters per hour -- through the ice sheet.
Drilling allowed for the installation of sensors for monitoring water flow and
ice motion.

“We’re the first people to actually go out and observe, and
drill to the bed,” Humphrey says.

The logistical difficulty of accessing the bed of the
Greenland ice sheet has limited researchers’ ability to fully understand this
drainage system’s response to surface ice melt, Humphrey says. As a result,
geologists have been forced to interpret Greenland’s velocity changes based on
theory developed from 40 years of observations on smaller, more accessible
mountain glaciers.

Mountain glacier geometry generally promotes rapid
development of water-draining basal conduits through melt-back of the overlying
ice roof. In contrast, conditions beneath much of Greenland do not support such
fast growth of the basal drainage system through ice melting, Humphrey
says.

“Our research suggests that, because of geometric
differences between the Greenland ice sheet and mountain glaciers, key aspects
of the (previous) theory are not directly transferrable,” Humphrey says. “It
requires a total rethinking of how the mechanism works.”

Still, questions persist.

Ice comes off of Greenland in two ways, Humphrey says. The
ice either deforms or slides off.

“The sliding of the ice is all related to the basal
drainage,” Humphrey says. “It’s a very complicated system we don’t understand.
It’s like the ice is floating.”

The National Science Foundation (NSF) and the Greenland
Analogue Project (GAP),
a consortium of Canadian, Finnish and Swedish companies (with contributions
from Britain and Denmark), provided $1.3 million and $1.6 million,
respectively, to fund the research. The NSF is providing another $1.2 million
to continue the research, Humphrey says.

Photo:Neil Humphrey
(right), a UW professor of geology and geophysics, and Joel Harper, an
associate professor in the Department of Geosciences at the University of
Montana, monitor drilling progress into the Greenland ice sheet. The two contributed to a research paper that is
published in the journal Science this month. (Toby Meierbachtol Photo)